Sodium-sulphur cell, method of operating same and method of load levelling using the same

Abstract

In a sodium-sulphur cell, liquid sodium is anodic reactant, sulphur and sodium polysulphide are cathodic reactants and sodium ions are conducted by a solid electrolyte. To increase cell capacity and improve safety, a storage region for cathodic reactants is provided away from said solid electrolyte and containing said cathodic reactants in the form of two contacting layers of immiscible liquids formed by gravitational separation. Liquid sulphur being stored does not contact the solid electrolyte. The sodium may also be stored out of contact with the electrolyte. Capillary-action means for feeding the sodium polysulphide from the two liquid layers to the cathode reaction, and for feeding sodium to the anode reaction are included.

What is claimed is: 
     
       1. Sodium-sulphur cell having: (a) an anodic reaction zone,   (b) sodium as anodic reactant,   (c) a cathodic reaction zone,   (d) a solid electrolyte disposed between said anodic and cathodic reaction zones for conducting Na +   ions,   (e) a storage region for cathodic reactants away from said cathodic reaction zone,   (f) sulphur and sodium polysulphide as cathodic reactants stored in said storage region in the form, at least when the cell is operational, of two contacting layers of immiscible liquids separated by gravitational separation, said stored reactants being out of contact with said cathodic reaction zone,   (g) means for feeding sodium polysulphide to and fro between said cathodic reaction zone and said storage region,   said storage region and said cathodic reaction zone being so connected as to permit sulphur vapour from the storage region to reach the cathodic reaction zone.   
     
     
       2. Sodium-sulphur cell according to claim 1, wherein said storage region and said cathodic reaction zone are connected by a vertically extending zone up which sulphur vapour passes to reach the cathodic reaction zone from the storage region. 
     
     
       3. Sodium-sulphur cell according to claim 1, wherein said means for feeding sodium polysulphide comprises capillary-action means by which said polysulphide moves from said contacting liquid layers to said cathodic reaction zone. 
     
     
       4. Sodium-sulphur cell according to claim 3, wherein said capillary-action means is mesh. 
     
     
       5. Sodium-sulphur cell according to claim 4, wherein said mesh is metal mesh. 
     
     
       6. Sodium-sulphur cell according to claim 1, further having a storage region for said sodium away from said anodic reaction zone, whereby stored sodium is maintained out of contact with said anodic reaction zone, and means for feeding liquid sodium to said anodic reaction zone. 
     
     
       7. Sodium sulphur cell according to claim 6, wherein both said storage regions are below the level of both said reaction zones. 
     
     
       8. Sodium sulphur cell according to claim 6, wherein said sodium feeding means comprises capillary-action means by which liquid sodium from said sodium storage region moves to said anodic reaction zone. 
     
     
       9. Sodium sulphur cell according to claim 8 wherein said capillary-action means is metal mesh. 
     
     
       10. In a sodium-sulphur cell in which liquid sodium is anodic reactant, sulphur and sodium polysulphide are cathodic reactants and sodium ions are conducted by a solid electrolyte, the improvement of a storage region for cathodic reactants away from said solid electrolyte containing said cathodic reactants in the form of two contacting layers of immiscible liquids formed by gravitational separation, whereby liquid sulphur being stored does not contact the solid electrolyte. 
     
     
       11. Sodium-sulphur cell according to claim 10, having capillary-action means for feeding said sodium polysulphide from said two liquid layers to the cathode reaction at said solid electrolyte. 
     
     
       12. Sodium-sulphur cell according to claim 10, wherein said liquid sodium is stored away from said solid electrolyte, whereby in the event of breakage of the solid electrolyte the stored anodic and cathodic reactants do not meet. 
     
     
       13. Sodium-sulphur cell having (a) an anodic reaction zone,   (b) liquid sodium as anodic reactant,   (c) a cathodic reaction zone,   (d) liquid sulphur and liquid sodium polysulphide as cathodic reactants,   (e) a solid electrolyte disposed between said anodic and cathodic reaction zones for conducting Na +  ions, wherein at least one of said liquid sodium and said cathodic reactants is stored away from said solid electrolyte, said cell further comprising     (f) shutter means operable to isolate said liquid sodium from said cathodic reactants, to prevent accidental mixing thereof.   
     
     
       14. Sodium-sulphur cell according to claim 13, having (a) vibration-sensing means arranged to operate said shutter means to effect isolation of the reactants when a vibration level beyond a predetermined threshold level is detected.   
     
     
       15. Sodium-suphur cell according to claim 13, wherein both said liquid sodium and said cathodic reactants are stored away from said solid electrolyte and two said shutter means are located to isolate respectively said liquid sodium and said cathodic reactants from said solid electrolyte. 
     
     
       16. Method of operating a sodium-sulphur cell having an anodic reaction zone, a cathodic reaction zone and a solid electrolyte conducting Na +   ions between said reaction zones, comprising the operations of (a) providing liquid sodium at said anodic reaction zone,   (b) storing liquid sulphur and liquid sodium polysulphide at a cathodic reactant storage location away from said cathodic reaction zone in the form of two contacting liquid layers of immiscible liquids,   (c) permitting sulphur vapour to pass to said cathodic reaction zone from said storage location as required by the cell operating mode,   (d) providing transfer of liquid sulphur from said cathodic reaction zone to said storage location as required by the cell operating mode,   (e) providing transfer of said liquid polysulphide to and fro between said storage location and said cathodic reaction zone as required by the cell operating mode, and   (f) preventing said liquid sulphur from passing to said cathodic reaction zone.   
     
     
       17. Method according to claim 16, wherein said operation (a) is performed by the operation of (i) storing liquid sodium at a sodium storage location away from said anodic reaction zone, and   (ii) providing transfer of the liquid sodium to and fro between said sodium storage location and said anodic reaction zone as required by the cell operating mode.   
     
     
       18. Method according to claim 16, wherein said operation (e) is performed by capillary action. 
     
     
       19. Method according to claim 17, wherein said operation (ii) is performed by capillary action. 
     
     
       20. Method according to claim 16 including maintaining said reaction zones and said cathodic reactant storage location at substantially the same temperature at any time. 
     
     
       21. Method of storing electrical power to provide load levelling comprising charging at least one sodium-sulphur cell during a first portion of a given twenty-four hour period and discharging said cell during a subsequent portion of said twenty-four hour period, said sodium sulphur cell having: (a) an anodic reaction zone,   (b) sodium as anodic reactant,   (c) a cathodic reaction zone,   (d) a solid electrolyte disposed between said anodic and cathodic reaction zones for conducting Na +  ions,   (e) a storage region for cathodic reactants away from said cathodic reaction zone,   (f) sulphur and sodium polysulphide as cathodic reactants stored in said storage region in the form, at least when the cell is operational, of two contacting layers of immiscible liquids separated by gravitational separation, said stored reactants being out of contact with said cathodic reaction zone,   (g) means for feeding sodium polysulphide to and fro between said cathodic reaction zone and said storage region, said storage region and said cathodic reaction zone being so connected as to permit sulphur vapour from the storage region to reach the cathodic reaction zone.